Acoustic imaging of diel vertical migration of zooplankton on the Newfoundland shelf

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Abstract

Diel vertical migration (DVM) of zooplankton is common to marine ecosystems around the world. Here, we examine the response of zooplankton vertical migration to hanging physical conditions using acoustic Doppler current pro filers (ADCPs) on the Newfoundland Shelf. Techniques for quantifying patterns of DVM in bioacoustics scattering layers are presented and evaluated, including both new methods and some taken from the literature. With these techniques, correlations of DVM patterns are examined in the horizontal, at scales of 10s of metres and 10s of kilometres, and an increase in correlation with proximity is found. Migrators are observed with high statistical significance (p < 0.05) to spend 10s of minutes more time at the surface in the morning and evening on overcast days than on clear days. Migration paths are coherent with isotherm depths at time scales longer than 20 days. Backscatter coefficient is modelled based on an empirical response to temperature and light.